Structural adaptation of halloysite to spheroidal morphology

Determine the structural mechanism by which halloysite, a kaolin-group 1:1 aluminosilicate with rolled-layer morphology, adapts to form spheroidal particles in weathered volcanic pumices and ashes, including how its kaolinite-like layers curve and organize in a spherical geometry and the roles of hydration, interlayer water, and cation exchange in enabling this shape.

Background

Halloysite commonly forms tubular and prismatic particles due to lattice mismatch between tetrahedral and octahedral sheets that induces layer curvature. In many volcanic weathering environments halloysite also occurs as spheroids, yet the mineral’s layered structure appears difficult to reconcile with a closed spherical geometry.

The review summarizes known morphologies (tubes, prisms, spheroids) and formation settings, noting that dehydration can convert tubes to prisms and that spheroids are frequent in highly saturated, confined precipitation spaces. Despite these observations, the specific structural pathway from layered halloysite to spheroidal particles has not been resolved.